Endothermic catalytic reactions are generally carried out in reaction spaces constructed in the shape of elongated tubes or pipes which are filled with a bulk particulate catalyst. The process medium to be processed by the endothermic reaction is introduced at one end of the catalytic pipe and discharged at the other end. These systems have the disadvantage of requiring trombones or expansion joints. The proposed system provides a large catalyst tube surface area within a small space, and eliminates the requirement for thermal expansion mechanisms.